Installing a plurality of semiconductor elements of one or more kinds in one container and modularizing them has found wide acceptance because the capacity is increased and because the labor needed to make wire connections is reduced. For example, what is presently known as an IGBT module includes a single container in which a plurality of IGBT chips and a flywheel diode chip are mounted. Numerous aluminum bonding wires are brought out to make connections from main electrodes (such as emitter and cathode electrodes on the top surfaces of the element chips) and from control electrodes (such as gate electrodes). Accordingly, in this IGBT module, cooling is done only from the collector side on the bottom of each chip.
As described above, connections of the emitters of the IGBT module depends on aluminum wire bonding in which the aluminum wire has a diameter of about 300 .mu.m. Therefore, heat dissipation from the collector side is possible but heat dissipation from the emitter side is very poor. Consequently, current capacity is limited.
In recent years, more compact IGBT modules having greater capacity than conventional modules are required in industrial and vehicular applications. As the capacity of a module is increased, more IGBT chips must be integrated in the module. Hence, it is inevitable that the module itself must be made larger. Also, the number of aluminum wires bonded inside the module is inevitably increased and reaches from several tens to several hundreds. Therefore, reliability problems exist in the presence of vibration. In addition, the aluminum wires and terminals to which the Al wires are connected are lengthened. As a result of the increased lengths, their inductances increase. When a large current is turned off, a resulting voltage surge increases. This is disadvantageous in designing an apparatus.
In one possible solution, wire bonding is not used for emitter connections. Instead top emitter electrodes are held in contact with an emitter terminal board in a plane similar to the technique used in a flat type semiconductor device such as a GTO thyristor. However, where a plurality of IGBT chips and a flywheel diode are connected in parallel and brought into contact with each other under pressure by a common terminal board, any nonuniformity in the distance between the bottom surface of the common terminal board and each electrode on the top surface of each chip before the application of the pressure, then it is impossible to apply uniform pressure to all of the elements in the module. In consequence, uniform energization cannot be accomplished.